I have had conversations with people who had been trading real money for over a year — actively, daily, with leverage — who could not tell me what the underlying was. Not because they were stupid. Because nobody ever stopped and defined it, and after a certain point it becomes embarrassing to ask.
So here is the vocabulary, in plain English, with no assumed knowledge. This is not a strategy page and there is nothing to buy at the end of it. It is the set of words that lets you read everything else without guessing.
If you learn nothing else here, learn the first three. Almost every expensive mistake I have watched people make traces back to not really understanding one of them.
The three that matter most
Underlying
The underlying is the actual asset that a contract is based on.
If you buy an option on Tesla, Tesla stock is the underlying. If you trade an S&P 500 futures contract, the index is the underlying. The contract is not the asset — it is an agreement whose value is derived from the asset. Hence the next word.
Why it matters: when someone says "the underlying moved 2% but my position lost money," they are describing the entire reason options are their own discipline. The contract and the asset do not move in lockstep. If you do not have a word for the thing underneath, you cannot reason about the gap.
Derivative
A derivative is any financial instrument whose value is derived from something else. Options are derivatives. Futures are derivatives. CFDs are derivatives.
You are not holding the asset. You are holding a contract about the asset.
Why it matters: this single distinction explains why derivative positions can expire worthless, why they carry leverage, why time affects them, and why the risk profile is fundamentally different from owning shares. A share of Tesla does not have a deadline. An option on Tesla does.
Most retail blowups I have seen came from people trading derivatives while mentally modelling them as shares.
Contract
In options, one contract almost always represents 100 shares of the underlying.
This trips up more beginners than anything else on this page. If an option is quoted at $2.50, you do not pay $2.50. You pay $2.50 × 100 = $250 per contract. If someone tells you they "bought ten contracts," they have exposure to 1,000 shares of the underlying, not ten shares.
Why it matters: position sizing errors here are not subtle. They are 100x.
The mechanics of an option
Option
An option is a contract giving the buyer the right — but not the obligation — to buy or sell the underlying at a set price, before or at a set date. The seller of that contract has the obligation to fulfil it if the buyer exercises.
A call is the right to buy. A put is the right to sell. We cover what an option actually is in more depth on its own page.
The asymmetry between buyer and seller — right versus obligation — is the whole foundation. Buyers have capped losses and open-ended potential. Sellers have capped gains and, depending on the structure, much larger risk.
Strike price
The strike is the price at which the option can be exercised. It is fixed when the contract is created and never changes.
A $250 call on a stock trading at $240 gives you the right to buy at $250, regardless of where the stock actually goes. The strike is your reference point for everything else — whether the option has value, how much, and how sensitive it is.
Expiry (expiration)
The expiry is the date the contract ceases to exist. After it, the option is either exercised or worthless.
This is the feature with no equivalent in share ownership. You can be completely right about direction and still lose everything because you were right too late. Time is not neutral in derivatives — it is an active force working against the buyer and for the seller.
Premium
The premium is the price of the option — what the buyer pays and the seller receives.
It is not a deposit and it is not recoverable. The buyer pays it up front; it is gone. The seller collects it up front; it is theirs to keep, in exchange for taking on obligation. You can price one out to see how premium responds to strike, time and volatility before committing anything.
What the price is actually made of
Intrinsic value
Intrinsic value is the portion of an option's price that would survive if the contract expired right now. It is real, immediate value.
A $250 call when the stock is at $260 has $10 of intrinsic value per share ($1,000 per contract). If the stock is at $240, that same call has zero intrinsic value — exercising it would mean buying at $250 something you could buy at $240.
Extrinsic value (time value)
Extrinsic value is everything else — the part of the premium that is paid for possibility. Time remaining, expected movement, uncertainty.
Extrinsic value decays to zero by expiry. Always. Without exception.
Why it matters, and why this is the most important entry on this page: when you buy an option, you are buying something that is guaranteed to lose part of its value simply by time passing. Every day you hold, some extrinsic value evaporates whether the stock moves or not. Someone who does not know this word will hold a position that is "not doing anything," and quietly bleed out.
Conversely, the option seller's entire business model is collecting extrinsic value and waiting for it to decay. If you cannot name it, you cannot tell which side of that trade you are on.
In the money / at the money / out of the money
In the money (ITM) — the option has intrinsic value. A call whose strike is below the current price; a put whose strike is above it.
At the money (ATM) — the strike is at or very near the current price.
Out of the money (OTM) — no intrinsic value. All premium is extrinsic. These are the cheap-looking options that beginners are drawn to, and they are cheap precisely because they are unlikely to pay.
Collectively this is called moneyness.
Risk and sensitivity
The Greeks
The Greeks are the measures of how an option's price responds to different forces:
- Delta — sensitivity to the underlying's price movement
- Gamma — the rate at which delta itself changes
- Theta — the daily cost of time decay
- Vega — sensitivity to changes in implied volatility
They are covered properly here. For now, the thing to know is that these are not advanced optional extras. They are the dashboard. Trading options without them is driving with the instruments taped over.
Implied volatility (IV)
Implied volatility is the market's expectation of how much the underlying will move, expressed as a percentage and baked into the option's price.
High IV means options are expensive — the market expects movement. Low IV means they are cheap. Crucially, IV can collapse after an anticipated event (earnings, for example), causing an option to lose value even when the stock moves in your favour. This is called an IV crush, and it catches out an enormous number of first-time earnings traders.
Leverage
Leverage is controlling a large exposure with a small amount of capital.
One option contract controlling 100 shares is leverage. It magnifies gains and losses in the same proportion. Leverage is not inherently dangerous — misunderstood leverage is. If you do not know how much underlying exposure your position actually represents, you do not know your risk.
Margin
Margin is capital your broker requires you to hold against a position that carries obligation — typically short options or leveraged positions.
It is not the cost of the trade. It is collateral. If the position moves against you, the requirement can increase, and if you cannot meet it you get a margin call — your broker demanding more capital or closing the position for you.
Execution and market structure
Bid, ask and spread
The bid is the highest price a buyer is currently willing to pay. The ask (or offer) is the lowest price a seller will accept. The gap between them is the spread.
You generally buy at the ask and sell at the bid, which means you start every trade slightly behind. On thinly traded options, this gap can be wide enough to be the single largest cost in your trade — larger than commission, and far more often ignored.
Liquidity
Liquidity is how easily you can enter and exit at a fair price. It shows up as tight spreads and healthy volume.
Illiquid contracts look attractive because they can seem cheap. The problem arrives when you need to get out and there is nobody on the other side at a reasonable price.
Volume and open interest
Volume is how many contracts traded today. Open interest is how many contracts are currently open and outstanding.
Together they tell you whether a contract is genuinely active or a ghost town. Low open interest is a warning sign regardless of how appealing the strike looks.
Long and short
Long means you own it and profit if it rises. Short means you sold something you do not own and profit if it falls.
In options this gets layered: you can be long a call, short a call, long a put, short a put — four distinct positions with four different risk profiles. "Short" does not mean bearish by itself. A short put is a bullish position.
Exercise and assignment
Exercise is the option buyer using their right — converting the contract into the underlying position.
Assignment is what happens to the seller on the other side: they are obligated to deliver. Assignment can occur before expiry on American-style options, and it frequently surprises people who sold a contract and mentally filed it as finished.
Multi-leg / spread
A spread or multi-leg position combines two or more options into one structure — buying one and selling another to define risk, reduce cost, or target a specific outcome.
Verticals, strangles, condors, calendars, risk reversals. All of them are just combinations of the same building blocks defined above. Once the vocabulary here is solid, none of them are mysterious.
The trading-style words
These get used loosely and cause more confusion than they should.
Scalping — intraday, entering and exiting within minutes or hours. Highest intensity, highest failure rate.
Day trading — positions opened and closed within the same session. No overnight exposure.
Swing trading — positions held days to weeks, sometimes months. Reading daily and weekly structure rather than tick charts.
Position trading / investing — months to years. Lowest intensity, and historically the highest success rate for the broadest number of people.
These are not difficulty tiers of the same skill. They are different activities that happen to use the same charts.
Why this matters more than the next strategy
There is a reason this page exists rather than another setup guide.
When you do not have the vocabulary, every confident voice sounds equally credible. You cannot evaluate a claim about theta decay if you do not know what theta is. You cannot tell whether someone selling you a strategy understands it, or is repeating something they heard. You cannot even describe your own position accurately enough to work out why it lost money.
That is why this gap keeps traders stuck — not a lack of effort, and not a lack of screen time. A missing foundation that makes filtering impossible.
Learning these words is a weekend of work. It permanently changes what you are able to assess. And unlike almost everything else in this industry, it costs nothing.